Telephone number mapping is a system of unifying the international telephone number system of the public switched telephone network with the Internet addressing and identification name spaces. Internationally, telephone numbers are systematically organized by the E.164 standard, while the Internet uses the Domain Name System (DNS) for linking domain names to IP addresses and other resource information. Telephone number mapping systems provide facilities to determine applicable Internet communications servers responsible for servicing a given telephone number using DNS queries.
The most prominent standard for telephone number mapping is the E.164 Telephone Number Mapping (ENUM) standard. The ENUM standard uses special DNS record types to translate a telephone number into a Uniform Resource Identifier (URI) or IP address that can be used in Internet communications. Responsive to queries from clients in networks, such as Internet Protocol Multimedia Subsystem (IMS) networks, ENUM servers return Naming Authority Pointer Resource Records (NAPTRs). NAPTR records are most commonly used for applications in Internet communication session management, e.g., in the mapping of servers and user addresses in the Session Initiation Protocol (SIP). The NAPTR record corresponding to the subscriber URI contains the subscriber contact record information.
ENUM therefore functions as a mechanism for translating a telephone number into a domain name with the requested address or number associated with it. ENUM services have become the core of national and international session management protocols for Video/Voice over IP (VoIP). ENUM services are used by VoIP service providers around the world and are expected to be employed for inter-service-provider operability.
While the ENUM standard provides important services, in the competitive world of multimedia IP solutions, there is increasing pressure to improve infrastructure resiliency and cost structures. Physical ENUMs (pENUMs) are limited in the sense that they are fixed on the underlying computing and communications infrastructure, as compared to cloud infrastructures. Once a pENUM is in place, it is not very flexible, e.g., to accommodate changes in traffic loads or location changes.